If you're a dog parent, chances are pretty good that you've observed your dog running in their sleep and wondered what on earth is causing those sleeping legs to move so much. Well, wonder no more! We've got the low-down on what causes dog sleep running and other quirky canine sleep behaviors.

Running, Twitching, and Barking

Although it might seem that dog sleep running is a distinct behavior from the twitching, barking, and other vocalizations dogs also sometimes do in their sleep, the truth is that these behaviors are all related, which is why they often happen at the same time. Whether you have a dog running in their sleep, twitching, barking, whining, or all of the above, what you actually have is a dog that's dreaming.

Dogs' brains are structurally similar to those of humans, according to Psychology Today, and they go through the same electrical patterns that human brains go through during the sleep cycle. This includes rapid eye movement, otherwise known as REM sleep, during which dreaming occurs. Many dogs try to physically act out their dreams–which often involves reliving memories of what they did that day–and this is the cause of sleep running, barking, and twitching.

Sleep Position

You may have wondered why your dog always curls up in a ball when he lies down to sleep, even when it's not cold. According to Vetstreet, this behavior is an evolutionary holdover from their ancestors. In the wild, wolves and wild dogs curl up while sleeping in order to protect their vulnerable organs from an attack.

But if that's the case, then why do some dogs sleep on their backs with their bellies exposed? A small percentage of dogs are comfortable sleeping this way–Vetstreet estimates between five and ten percent. Easy-going, well-socialized dogs with temperaments that are a far cry from their wolf cousins and ancestors may favor that position. If your pup likes to sleep on their back, this is a sign that they trust you and feels safe and secure in their surroundings.

Turning Circles and Digging

Another strange behavior you might have observed during your dog's bedtime is a habit of scratching the floor and turning in circles before lying down, even on a soft surface like a bed or pillow. This behavior goes all the way back to the same nesting instinct that compels dogs to curl up to sleep. In the wild, their canine ancestors would dig to soften the ground and create nests to lie down in, which would offer added protection and help to regulate body temperature. They would also turn circles to tamp down the dirt, leaves, or grass lining of their bed to make it more comfortable. Why this instinct has survived thousands of years and is still strong in domestic dogs today remains a mystery.